RNA cleavage is a fundamental and ancient host response for controlling viral infections in both plants and animals. In higher vertebrates, including humans, RNA cleavage as a means of controlling viruses is mediated by the type I interferons (IFN) through its effector, the uniquely regulated endoribonuclease, RNase L. RNase L is activated by unusual 2',5'-linked oligoadenylates (2-5A) produced during viral infections. 2-5A activates RNase L resulting in cleavage of host and viral RNAs within single stranded regions, predominantly after UU and UA. As a result of its specificity, RNase L produces small, highly structured RNA cleavage products. In 2007 we reported that RNA cleavage products obtained from digestion of self RNA by RNase L activated RIG-I-like receptors (RLR) resulting in amplification of type I IFN synthesis. These RNA cleavage products represent a novel class of small RNA molecules named "Suppressor of Virus RNA" (svRNA). Our GOALS in this project are to clone, identify and probe the functions of svRNAs generated from both host RNA and from viral [hepatitis C virus (HCV)] RNA. Our HYPOTHESIS is that svRNAs are essential to host defense against a wide range of viruses that are pathogenic for humans. Our Specific Aims are: (1) to isolate and identify svRNA liberated by RNase L from host and viral RNA, we will cleave HCV RNA with purified RNase L and clone small RNAs that bind to RLRs, and cleave cellular (self) RNA in intact cells treated with 2-5A and clone small RNAs that bind to RLRs;(2) To characterize activation of RIG-I and MDA5 by svRNAs we will perform ATPase activation studies, determine the kinetic parameters for svRNA interactions with RIG-I and MDA5 by surface plasmon resonance, measure conformational changes in RIG-I and MDA5, and establish the sequence and structural requirement of svRNA for activation of RIG-I and MDA5;and (3) to determine the role of svRNA in antiviral innate immunity we will identify svRNAs in HCV infected cells, and determine the antiviral effects of svRNAs in mice. Our recent studies suggest an essential role of svRNAs in the antiviral state in higher vertebrates. In the proposed studies we seek to obtain a fundamental understanding of this important pathway as it relates to host defense against viruses. Therefore, there are cogent and health-related justifications for these studies. PUBLIC HEALTH RELEVANCE: We have identified a novel type of small RNA that amplifies and perpetuates interferon production, the body's frontline defense against a broad-range of different types of viruses. In the proposed studies, we will identify and characterize these small RNAs and we will use them to inhibit virus infections. The knowledge to be gained from the proposed studies could contribute to improved treatments for viral infections.